Flash-back of laminar premixed methane/air flames on slit and tube burners

Flash-back of laminar methane/air flames on slit and tube burners in a wide range of burner widths and with equivalence ratios between 0.9 and 1.2 is investigated. A comparison between measured and calculated values of the critical gradients shows that the critical gradients predicted by the numerical model do not deviate more than 10% from the measured critical gradients for burners with a width/diameter ranging from 4 to 10mm and with equivalence ratios between 0.9 and 1.1. The maximum difference between the computed critical gradients of the slit and the tube burner flames is approximately 10% at a width/diameterof 4mm. The differences are not visible in the experimental data because of experimental inaccuracies. For burners sizes larger than 6 mm the differences almost vanish. An analytical model which described the decrease of the critical gradient as a function of the burner width/diameter shows that this increase is mainly caused by the curvature of the parabolic velocity profile near the burner wall